Instant Messaging (IM) is a form of real-time communication between two or more people based on typed text, recorded or real-time voice with or without video. The messages are conveyed via computers connected over a network such as the Internet. IM systems typically include a presence server that collects and distributes presence information. In some cases, IM systems also collect and distribute presence information via a distributed peer-to-peer (“P2P”) communication network in addition to, or instead of, a presence server. Presence information may indicate where a person is located, whether he currently accepts messages from others, etc. Presence information may change frequently and is typically of interest to a large number of users. As a result, the presence service is constantly distributing presence updates to a large number of clients, and each client frequently receives and processes presence updates of other clients.
In a wired network, PCs run on outlet power and are always on. Hence, the cost of receiving and processing presence updates is low in terms of power consumption. However, in a wireless network, mobile devices have limited power resources, and the cost associated with frequent presence updates is high because mobile devices have to come out of power-save mode in order to receive and process incoming presence updates.